function add(i) {
    i++;
    return i;
}
function sub(i) {
    if (i <= 0) {
        i = 0;
    }
    else {
        i--;
    }
    return i;   
}
function area(radius) {
    return Math.PI * radius * radius;
}
function circumference(radius) {
    return 2 * Math.PI * radius;
}
export { add, sub, area, circumference }
  